gravity and frictional drag create a balance called terminal velocity. a falling object no longer has an acceleration because gravity is balanced by friction. so in order for a rain drop to fall and overcome terminal velocity it must be kinda large.

Collision-Coalescense Process

generates precipitation. begins with large droplets with high terminal velocities. the collector droplets collide with smaller droplets. compressed air forces the smaller droplets outside. and the collector drops capture the larger cloud drops.

Coalescence Efficiency

tends to be very high because most of the droplets are coalessed into the collector drop and are unable to escape.

Bergeron Process

saturation vapor pressure of ice is less than super cooled water. when both are present, the super cooled water will be deposited onto the ice because the ice has a lower pressure causing the ice crystals to grow rapidly. the falling of the ice crystals and water creates riming and aggregation.

Riming

when ice crystals fall through a cloud and collide with supercooled droplets, the liquid water freezes onto them.